Extending path computation element protocol to accommodate routing and wavelength assignment in wavelength switched optical networks

ABSTRACT

A network component comprising at least one processor configured to implement a method comprising transmitting a request to compute a routing assignment, a wavelength assignment, or both for a signal in a wavelength switched optical network, wherein the request comprises a lightpath constraint and wherein the request is transmitted using a path computation element protocol. Also disclosed is a network comprising a first path computation element (PCE) and a path computation client (PCC) in communication with the PCE, wherein the PCC is configured to send a request to and receive a reply from the PCE using a PCE protocol, wherein the request comprises a lightpath constraint. Included is a method comprising sending a discovery advertisement to the at least one PCE that calculates a wavelength assignment, receiving a response comprising a PCE capability information from the PCE, wherein the request and the reply are communicated via a PCE protocol.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of prior U.S. patent application Ser.No. 12/138,144 filed Jun. 12, 2008 by Lee et al. and entitled “ExtendingPath Computation Element Protocol to Accommodate Routing and WavelengthAssignment in Wavelength Switched Optical Networks”, which claimspriority to U.S. Provisional Patent Application No. 60/974,278 filedSep. 21, 2007 by Lee et al. and entitled “Method for Extending PCEP toAccommodate Routing and Wavelength Assignment in Wavelength SwitchedOptical Networks”, both of which are incorporated herein by reference asif reproduced in their entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

REFERENCE TO A MICROFICHE APPENDIX

Not applicable.

BACKGROUND

Wavelength division multiplexing (WDM) is one technology that isenvisioned to increase bandwidth capability and enable bidirectionalcommunications in optical networks. In WDM networks, multiple datasignals can be transmitted simultaneously between network elements (NEs)using a single fiber. Specifically, the individual signals may beassigned different transmission wavelengths so that they do notinterfere or collide with each other. The path that the signal takesthrough the network is referred to as the lightpath. One type of WDMnetwork, a wavelength switched optical network (WSON), seeks to switchthe optical signals with fewer optical-electrical-optical (OEO)conversions along the lightpath, e.g. at the individual NEs, thanexisting optical networks.

One of the challenges in implementing WDM networks is the determinationof the routing and wavelength assignment (RWA) for the various signalsthat are being transported through the network at any given time. Unliketraditional circuit-switched and connection-oriented packet-switchednetworks that merely have to determine a route for the data streamacross the network, WDM networks are burdened with the additionalconstraint of having to ensure that the same wavelength is notsimultaneously used by two signals over a single fiber. This constraintis compounded by the fact that WDM networks typically use specificoptical bands comprising a finite number of usable optical wavelengths.As such, the RWA continues to be one of the challenges in implementingWDM technology in optical networks.

SUMMARY

In one embodiment, the disclosure includes a network componentcomprising at least one processor configured to implement a methodcomprising transmitting a request to compute a routing assignment, awavelength assignment, or both for a signal in a WSON, wherein therequest comprises a lightpath constraint, and wherein the request istransmitted using a path computation element protocol.

In another embodiment, the disclosure includes a network comprising apath computation element (PCE) and a path computation client (PCC) incommunication with the PCE, wherein the PCC is configured to send arequest to and receive a reply from the PCE using a PCE protocol,wherein the request comprises a lightpath constraint.

In yet another embodiment, the disclosure includes a method comprisingsending a discovery advertisement to the at least one PCE thatcalculates a wavelength assignment, receiving a reply comprising a PCEcapability information from the PCE, wherein the request and the replyare communicated via a PCE protocol.

These and other features will be more clearly understood from thefollowing detailed description taken in conjunction with theaccompanying drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of this disclosure, reference is nowmade to the following brief description, taken in connection with theaccompanying drawings and detailed description, wherein like referencenumerals represent like parts.

FIG. 1 is a schematic diagram of an embodiment of a WSON system.

FIG. 2 is a protocol diagram of an embodiment of the communicationsbetween a PCE and a PCC.

FIG. 3 is a schematic diagram of an embodiment of a PCE architecture.

FIG. 4 is a schematic diagram of another embodiment of the PCEarchitecture.

FIG. 5 is a schematic diagram of another embodiment of the PCEarchitecture.

FIG. 6 is a schematic diagram of an embodiment of a lightpath routeparameter type length value (TLV).

FIG. 7 is a schematic diagram of an embodiment of a wavelength selectionpreference TLV.

FIG. 8 is a schematic diagram of an embodiment of a general-purposecomputer system.

DETAILED DESCRIPTION

It should be understood at the outset that although an illustrativeimplementation of one or more embodiments are provided below, thedisclosed systems and/or methods may be implemented using any number oftechniques, whether currently known or in existence. The disclosureshould in no way be limited to the illustrative implementations,drawings, and techniques illustrated below, including the exemplarydesigns and implementations illustrated and described herein, but may bemodified within the scope of the appended claims along with their fullscope of equivalents.

Disclosed herein is a system and method for extending path computationelement protocol (PCEP) to accommodate RWA in WDM networks, such as theWSON. Specifically, a PCC may send a request to a PCE using PCE protocol(PCEP). The request may include various types of lightpath constraints,such as a RWA computation option, a route parameter, a wavelengthselection preference, an optimization degree, a timelinesscharacteristic, a duration, or combinations thereof. The lightpathconstraints may be used in the computation of the RWA, and the RWA maybe returned to the PCC using a PCEP reply.

FIG. 1 illustrates one embodiment of a WSON system 100. The system 100may comprise a WSON 110, a control plane controller 120, and a PCE 130.The WSON 110, control plane controller 120, and PCE 130 may communicatewith each other via optical, electrical, or wireless means. The WSON 110may comprise a plurality of NEs 112 coupled to one another using opticalfibers. In an embodiment, the optical fibers may also be considered NEs112. The optical signals may be transported through the WSON 110 overlightpaths that may pass through some of the NEs 112. In addition, someof the NEs 112, for example those at the ends of the WSON 110, may beconfigured to convert between electrical signals from external sourcesand the optical signals used in the WSON 110. Although four NEs 112 areshown in the WSON 110, the WSON 110 may comprise any number of NEs 112.

The WSON 110 may be any optical network that uses active or passivecomponents to transport optical signals. The WSON 110 may implement WDMto transport the optical signals through the WSON 110, and may comprisevarious optical components as described in detail below. The WSON 110may be part of a long haul network, a metropolitan network, or aresidential access network.

The NEs 112 may be any devices or components that transport signalsthrough the WSON 110. In an embodiment, the NEs 112 consist essentiallyof optical processing components, such as line ports, add ports, dropports, transmitters, receivers, amplifiers, optical taps, and so forth,and do not contain any electrical processing components. Alternatively,the NEs 112 may comprise a combination of optical processing componentsand electrical processing components. At least some of the NEs 112 maybe configured with wavelength converters, optical-electrical (OE)converters, electrical-optical (EO) converters, OEO converters, orcombinations thereof. However, it may be advantageous for at least someof the NEs 112 to lack such converters as such may reduce the cost andcomplexity of the WSON 110. In specific embodiments, the NEs 112 maycomprise optical cross connects (OXCs), photonic cross connects (PXCs),type I or type II reconfigurable optical add/drop multiplexers (ROADMs),wavelength selective switches (WSSs), fixed optical add/dropmultiplexers (FOADMs), or combinations thereof.

The NEs 112 may be coupled to each other via optical fibers. The opticalfibers may be used to establish optical links and transport the opticalsignals between the NEs 112. The optical fibers may comprise standardsingle mode fibers (SMFs) as defined in ITU-T standard G.652, dispersionshifted SMFs as defined in ITU-T standard G.653, cut-off shifted SMFs asdefined in ITU-T standard G.654, non-zero dispersion shifted SMFs asdefined in ITU-T standard G.655, wideband non-zero dispersion shiftedSMFs as defined in ITU-T standard G.656, or combinations thereof. Thesefiber types may be differentiated by their optical impairmentcharacteristics, such as attenuation, chromatic dispersion, polarizationmode dispersion, four wave mixing, or combinations thereof. Theseeffects may be dependent upon wavelength, channel spacing, input powerlevel, or combinations thereof. The optical fibers may be used totransport WDM signals, such as course WDM (CWDM) signals as defined inITU-T G.694.2 or dense WDM (DWDM) signals as defined in ITU-T G.694.1.All of the standards described herein are incorporated herein byreference.

The control plane controller 120 may coordinate activities within theWSON 110. Specifically, the control plane controller 120 may receiveoptical connection requests and provide lightpath signaling to the WSON110 via an Interior Gateway Protocol (IGP) such as GeneralizedMulti-Protocol Label Switching (GMPLS), thereby coordinating the NEs 112such that data signals are routed through the WSON 110 with little or nocontention. In addition, the control plane controller 120 maycommunicate with the PCE 130 using PCEP, provide the PCE 130 withinformation that may be used for the RWA, receive the RWA from the PCE130, and/or forward the RWA to the NEs 112. The control plane controller120 may be located in a component outside of the WSON 110, such as anexternal server, or may be located in a component within the WSON 110,such as a NE 112.

The PCE 130 may perform all or part of the RWA for the WSON system 100.Specifically, the PCE 130 may receive the wavelength or otherinformation that may be used for the RWA from the control planecontroller 120, from the NEs 112, or both. The PCE 130 may process theinformation to obtain the RWA, for example, by computing the routes,e.g. lightpaths, for the optical signals, specifying the opticalwavelengths that are used for each lightpath, and determining the NEs112 along the lightpath at which the optical signal should be convertedto an electrical signal or a different wavelength. The RWA may includeat least one route for each incoming signal and at least one wavelengthassociated with each route. The PCE 130 may then send all or part of theRWA information to the control plane controller 120 or directly to theNEs 112. To assist the PCE 130 in this process, the PCE 130 may comprisea global traffic-engineering database (TED), a RWA information database,an optical performance monitor (OPM), a physical layer constraint (PLC)information database, or combinations thereof. The PCE 130 may belocated in a component outside of the WSON 110, such as an externalserver, or may be located in a component within the WSON 110, such as aNE 112.

In some embodiments, the RWA information may be sent to the PCE 130 by apath computation client (PCC). The PCC may be any client applicationrequesting a path computation to be performed by the PCE 130. The PCCmay also be any network component that makes such a request, such as thecontrol plane controller 120, or any NE 112, such as a ROADM or a FOADM.

FIG. 2 illustrates an embodiment of a path computation communicationmethod 200 between the PCC and the PCE. The method 200 may beimplemented using any suitable protocol, such as the PCEP. In the method200, the PCC may send a path computation request 202 to the PCE. Therequest may include any of the lightpath constraints disclosed below. At204, the PCE calculates a path through the network that meets thelightpath constraints. For example, the PCE may calculate the RWA. ThePCE may then send a path computation reply 206 to the PCC. The reply 206may comprise the RWA or one of the other reply options described below.

When a network comprises a plurality of PCEs, not all PCEs within thenetwork may have the ability to calculate the RWA. Therefore, thenetwork may comprise a discovery mechanism that allows the PCC todetermine the PCE in which to send the request 202. For example, thediscovery mechanism may comprise an advertisement from a PCC for aRWA-capable PCE, and a response from the PCEs indicating whether theyare RWA-capable. The discovery mechanism may be implemented as part ofthe method 200 or as a separate process.

The PCE may be embodied in one of several architectures. FIG. 3illustrates an embodiment of a combined RWA architecture 300. In thecombined RWA architecture 300, the PCC 310 communicates the RWA requestand the required information to the PCE 320, which implements both therouting assignment and the wavelength assignment functions using asingle computation entity, such as a processor. For example, theprocessor may process the RWA information using a single or multiplealgorithms to compute the lightpaths as well as to assign the opticalwavelengths for each lightpath. The amount of RWA information needed bythe PCE 320 to compute the RWA may vary depending on the algorithm used.If desired, the PCE 320 may not compute the RWA until sufficient networklinks are established between the NEs or when sufficient RWA informationabout the NEs and the network topology is provided. The combined RWAarchitecture 300 may be preferable for network optimization, smallerWSONs, or both.

FIG. 4 illustrates an embodiment of a separated RWA architecture 400. Inthe separated RWA architecture 400, the PCC 410 communicates the RWArequest and the required information to the PCE 420, which implementsboth the routing function and the wavelength assignment function usingseparate computation entities, such as processors 422 and 424.Alternatively, the separated RWA architecture 400 may comprise twoseparate PCEs 420 each comprising one of the processors 422 and 424.Implementing routing assignment and wavelength assignment separately mayoffload some of the computational burden on the processors 422 and 424and reduce the processing time. In an embodiment, the PCC 410 may beaware of the presence of only one of two processors 422, 424 (or twoPCEs) and may only communicate with that processor 422, 424 (or PCE).For example, the PCC 410 may send the RWA information to the processor422, which may compute the lightpath routes and forward the routingassignment to the processor 424 where the wavelength assignments areperformed. The RWA may then be passed back to the processor 422 and thento the PCC 410. Such an embodiment may also be reversed such that thePCC 410 communicates with the processor 424 instead of the processor422.

In either architecture 300 or 400, the PCC may receive a route from thesource to destination along with the wavelengths, e.g. GMPLS generalizedlabels, to be used along portions of the path. The GMPLS signalingsupports an explicit route object (ERO). Within an ERO, an ERO labelsub-object can be used to indicate the wavelength to be used at aparticular NE. In cases where the local label map approach is used, thelabel sub-object entry in the ERO may have to be translated.

FIG. 5 illustrates a distributed wavelength assignment architecture 500.In the distributed wavelength assignment architecture 500, the PCE 510may receive some or all of the RWA information from the NEs 520, 530,and 540, perhaps via direct link, and implements the routing assignment.The PCE 510 then directly or indirectly passes the routing assignment tothe individual NEs 520, 530, and 540, which assign the wavelengths atthe local links between the NEs 520, 530, and 540 based on localinformation. Specifically, the NE 520 may receive local RWA informationfrom the NEs 530 and 540 and send some or all of the RWA information tothe PCE 510. The PCE 510 may compute the lightpaths using the receivedRWA information and send the list of lightpaths to the NE 520. The NE520 may use the list of lightpaths to identify the NE 530 as the next NEin the lightpath. The NE 520 may establish a link to the NE 530 and usethe received local RWA information that may comprise additionalconstraints to assign a wavelength for transmission over the link. TheNE 530 may receive the list of lightpaths from the NE 520, use the listof lightpaths to identify the NE 540 as the next NE in the lightpath,establish a link to the NE 540, and assign the same or a differentwavelength for transmission over the link. Thus, the signals may berouted and the wavelengths may be assigned in a distributed mannerbetween the remaining NEs in the network. Assigning the wavelengths atthe individual NEs may reduce the amount of RWA information that has tobe sent to the PCE 510.

As mentioned above, the request may comprise at least one lightpathconstraint. The lightpath constraint may be any parameter that affectsor limits the use of wavelengths along the lightpaths within thenetwork. In an embodiment, the lightpath constraints may include a RWAcomputation option. The RWA computation option may specify the portionsof the RWA that needs to be solved or otherwise considered. Suitable RWAcomputation options include routing assignment, wavelength assignment,routing and wavelength assignment, and routing assignment with asuggested or restricted wavelength set. Routing assignment may indicatethat the NE desires the routing assignment, but not the wavelengthassignment. Alternatively, routing assignment may indicate that therouting assignment is separated from the wavelength assignment, asindicated in FIG. 4 above. In either case, the request may comprise thewavelength assignment. Wavelength assignment may indicate that the NEdesires the routing assignment, but not the wavelength assignment.Alternatively, wavelength assignment may indicate that the wavelengthassignment is separated from the routing assignment, as indicated inFIG. 4 above. In either case, the request may comprise the routingassignment. Routing and wavelength assignment may indicate that the NEdesires both the routing assignment and the wavelength assignment or amore optimal RWA. Finally, routing assignment with a suggested orrestricted wavelength set may indicate that the NE desires the routingassignment and a suggested or restricted set of wavelengths such ascandidate wavelengths from which the NE may select the wavelengths toassign to the lightpath(s). Alternatively, routing assignment with asuggested or restricted wavelength set may indicate that the wavelengthassignment is distributed, as indicated in FIG. 5 above.

In a specific embodiment, the RWA computation option may be included ina request parameter (RP) object in the request. For example, the RWAcomputation option may be embodied as a RWA Computation (RC) flaglocated in the flags field of the RP object. In an embodiment, the RCflag may be defined as indicated in Table 1 below.

TABLE 1 Bit Description 00 Routing Assignment 01 Wavelength Assignment10 Routing Assignment with Suggested or Restricted Wavelength Set 11Routing and Wavelength Assignment

In an embodiment, the lightpath constraints may include a routeparameter. The route parameter may indicate a limitation in theassignment of wavelengths to the lightpath. Suitable route parameteroptions include bidirectional assignment of wavelengths, simultaneousassignment of wavelengths to a primary lightpath and a backup lightpath,and optical transmitter tuning range constraints. Bidirectionalassignment of wavelengths may indicate that a single wavelength shouldbe assigned to a lightpath and used for two-way communications or thatseparate wavelengths should be assigned to each direction of thelightpath. Simultaneous assignment of wavelengths to a primary lightpathand a backup lightpath may indicate that the same wavelength should beassigned to the primary lightpath and the backup lightpath.Alternatively, simultaneous assignment of wavelengths to a primarylightpath and a backup lightpath may indicate that separate wavelengthsshould be assigned to the primary lightpath and the backup lightpath.The optical transmitter tuning range constraint may indicate thewavelengths at which any optical transmitters along the lightpath cantransmit.

In a specific embodiment, the route parameter may be included in a RPobject in the request. For example, when the RC flag described aboveindicates wavelength assignment, an optional route parameter TLV may beincluded in the RP object. FIG. 6 illustrates one embodiment of asuitable route parameter TLV 600. The TLV 600 may include a type field602, a length field 604, and a value field 606. The type field 602 maycomprise the first about 16 bits of the TLV 600, and may indicate thatthe TLV 600 is a route parameter TLV. The length field 604 may be thesubsequent about 16 bits of the TLV 600, and may indicate the length ofthe value field 606. The value field 606 may be any size, but in someembodiments is the subsequent about 32 bits on the TLV 600 and mayindicate the route parameter. In some instances, the value field 606 maycomprise one or more flags, such as an I flag 608 and an S flag 610. TheI flag 608 may be about 1 bit in length, and may indicate thedirectionality of the wavelength assignment. For example, the TLV 600may indicate a bidirectional assignment of wavelengths when the I flagis set to zero, and the TLV 600 may indicate a unidirectional assignmentof wavelengths when the I flag is set to one. Similarly, the S flag 610may be about 1 bit in length, and may indicate the commonality of thewavelength assignment. For example, the TLV 600 may indicate anassignment of the same wavelength to the primary and backup lightpathswhen the S flag is set to zero, and the TLV 600 may indicate anassignment of different wavelengths to a primary path and a backup pathwhen the S flag is set to one.

In an embodiment, the lightpath constraints may include a wavelengthselection preference. The wavelength selection preference may indicatethe criteria by which the wavelength assignment is assigned to thelightpath. Suitable wavelength selection preference options includerandom, first fit, most used, least loaded, and no preference. Randommay indicate that the wavelength should be randomly chosen from a groupof suitable wavelengths. First fit may indicate that the wavelengthshould be the first suitable wavelength that is found. Most used mayindicate that the selected wavelength should be the most commonly usedwavelength within the group of all suitable wavelengths. Least loadedmay indicate that the selected wavelength should be the least commonlyused wavelength within the group of all suitable wavelengths. Finally,no preference may indicate that the PCC does not care or has no opinionas to the selected wavelength assignment.

In a specific embodiment, the wavelength selection preference may beincluded in the RP object in the request. For example, when the RC flagin the RP object described above indicates wavelength assignment, anoptional wavelength selection preference TLV may be included in the RPobject. FIG. 7 illustrates one embodiment of a suitable wavelengthselection preference TLV 700. The TLV 700 may include a type field 702,a length field 704, and a value field 706. The type field 702 maycomprise the first about 16 bits of the TLV 700, and may indicate thatthe TLV 700 is a wavelength selection TLV. The length field 704 may bethe subsequent about 16 bits of the TLV 700, and may indicate the lengthof the value field 706. The value field 706 may be any size, but in someembodiments is the subsequent about 32 bits of the TLV 700 and mayindicate the wavelength selection preference as indicated in Table 2below.

TABLE 2 Function Code Wavelength Selection Preference 1 Random 2 FirstFit 3 Most Used 4 Least Loaded 5 No Preference

In an embodiment, the lightpath constraints may include an optimizationdegree. The optimization degree may indicate the number of lightpathsthat are included in a single RWA calculation. Suitable optimizationdegree options include concurrent optimization, simultaneous request ofa primary lightpath and a backup lightpath, or sequential optimization.Concurrent optimization may indicate that multiple lightpaths arecontained in a single request. Simultaneous request of a primarylightpath and a backup lightpath may indicate that two lightpaths arerequested: a primary lightpath that is intended to carry the signal, anda backup lightpath that can carry the signal if the primary lightpathfails. The primary and the backup lightpaths may have completelydifferent routes, some common portions of their routes, or the sameroute. Similarly, the primary and the backup lightpaths may usecompletely different wavelengths, some common wavelengths if the networkcomprises at least one converter, or the same wavelength. While theprimary and backup lightpaths may share some or all of their routing andwavelength assignment, the primary and backup lightpaths generally donot have the exact same routing and wavelength assignment. If desired,the request may indicate whether the primary and backup lightpaths areto share routing assignment, wavelength assignment, or both, as well asthe extent of such. Sequential optimization may indicate that a singlelightpath is contained in the request.

In an embodiment, the lightpath constraints may include a timelinesscharacteristic. The timeliness characteristic may indicate theimportance of timeliness to the request or how quickly the RWA should becalculated. Suitable optimization degree options include time critical,soft time bounds, and scheduled. Time critical may indicate thattimeliness is important to the request, and may typically be used forrestoration of network services or for other high-priority real-timeservice requests. Soft time bounds may indicate that timeliness is ofmoderate importance to the request. Soft time bound requests should behandled in a responsive manner, but may allow sufficient time for someamount of network optimization. Soft time bounds may typically be usedfor new or first-time connection requests. Scheduled may indicate thattimeliness is not overly important to the request. Scheduled requestsmay be used for services requested prior to receipt of the signal, andmay receive the highest degree of network optimization.

In an embodiment, the lightpath constraints may include a duration. Theduration may indicate the length of the time in which the signal will bein service. Suitable duration options include dynamic, pseudo-static,and static. Dynamic may indicate that the signal will last a relativelyshort amount of time. Pseudo-static may indicate that the signal willlast a moderate amount of time. Static may indicate that the signal willlast a relatively long time.

After the request comprising the lightpath constraint has been receivedby the PCE, the PCE may issue a reply back to the PCC. The reply mayinclude the RWA computed subject to the lightpath constraints indicatedabove. In addition, the reply may include any or all of the lightpathconstraints that were contained in the request. If there is no RWA thatsatisfies the lightpath constraints, the reply may indicate such, forexample using a no path indicator. In a specific embodiment, the no pathindicator is contained in a no path vector TLV in a no path object inthe reply. Specifically, a 0x10 bit flag may be set in the no pathvector TLV to indicate that no route, wavelength, or both was found thatsatisfied the lightpath constraints in the request. Additionally oralternatively, the reply may indicate which parts of the RWA could notbe obtained. For example, the reply may indicate that a suitable routecould not be found, a suitable wavelength could not be found, or asuitable combination of a route and a wavelength could not be found.Finally, the reply may include a suggestion for relaxing the lightpathconstraints to obtain the RWA. For example, if the RWA would have beenobtainable but for the presence of one lightpath constraint, e.g.duration, then the reply may indicate such.

In an embodiment, the reply may contain at least one message. Forexample, if the PCE is not configured to calculate a RWA, then the replymay contain an error message that the PCE is not configured to calculatethe RWA. Such an error message may contain a PCEP error object and anerror-value, such as error-type=15 and the error-value=1. Alternatively,if the request is not compliant with administrative privileges, then thereply may contain an error message that indicates that the request isnot compliant with administrative privileges. Such an error message maycontain a PCEP-error object and an error-value, such as the error-type=6and the error-value=3. Further in the alternative, if the request or theRWA violates some policy within the PCE or the WSON, then the reply maycontain an error message that indicates the policy violation. Such anerror message may contain a PCEP error object, such as error-type=6. Inany event, the request may be cancelled, and a new request may have tobe sent to the PCE.

The network components described above may be implemented on anygeneral-purpose network component, such as a computer or networkcomponent with sufficient processing power, memory resources, andnetwork throughput capability to handle the necessary workload placedupon it. FIG. 8 illustrates a typical, general-purpose network component800 suitable for implementing one or more embodiments of the componentsdisclosed herein. The network component 800 includes a processor 802(which may be referred to as a central processor unit or CPU) that is incommunication with memory devices including secondary storage 804, readonly memory (ROM) 806, random access memory (RAM) 808, input/output(I/O) devices 810, and network connectivity devices 812. The processormay be implemented as one or more CPU chips, or may be part of one ormore application specific integrated circuits (ASICs).

The secondary storage 804 is typically comprised of one or more diskdrives or tape drives and is used for non-volatile storage of data andas an over-flow data storage device if RAM 808 is not large enough tohold all working data. Secondary storage 804 may be used to storeprograms that are loaded into RAM 808 when such programs are selectedfor execution. The ROM 806 is used to store instructions and perhapsdata that are read during program execution. ROM 806 is a non-volatilememory device that typically has a small memory capacity relative to thelarger memory capacity of secondary storage. The RAM 808 is used tostore volatile data and perhaps to store instructions. Access to bothROM 806 and RAM 808 is typically faster than to secondary storage 804.

While several embodiments have been provided in the present disclosure,it should be understood that the disclosed systems and methods might beembodied in many other specific forms without departing from the spiritor scope of the present disclosure. The present examples are to beconsidered as illustrative and not restrictive, and the intention is notto be limited to the details given herein. For example, the variouselements or components may be combined or integrated in another systemor certain features may be omitted, or not implemented.

In addition, techniques, systems, subsystems, and methods described andillustrated in the various embodiments as discrete or separate may becombined or integrated with other systems, modules, techniques, ormethods without departing from the scope of the present disclosure.Other items shown or discussed as coupled or directly coupled orcommunicating with each other may be indirectly coupled or communicatingthrough some interface, device, or intermediate component whetherelectrically, mechanically, or otherwise. Other examples of changes,substitutions, and alterations are ascertainable by one skilled in theart and could be made without departing from the spirit and scopedisclosed herein.

What is claimed is:
 1. A network component, comprising: a pathcomputation element (PCE) in communication with a path computationclient (PCC), wherein the PCE is configured to receive a request fromand send a reply to the PCC using PCE communication protocol (PCEP), andwherein the request comprises: a lightpath constraint that indicateslimits on wavelength usage along a lightpath; and a wavelength policyconstraint that specifies an operator's policy information forwavelength assignment, wherein the reply comprises a no path indicatorthat indicates that no lightpath was found.
 2. The network component ofclaim 1, wherein the wavelength policy constraint comprises a randomassignment wavelength selection preference.
 3. The network component ofclaim 1, wherein the wavelength policy constraint comprises a most usedwavelength selection preference.
 4. The network component of claim 1,wherein the wavelength policy constraint comprises a least usedwavelength selection preference.
 5. A network component, comprising: apath computation element (PCE) in communication with a path computationclient (PCC), wherein the PCE is configured to receive a request fromand send a reply to the PCC using PCE communication protocol (PCEP),wherein the request comprises: a lightpath constraint that indicateslimits on wavelength usage along a lightpath; and a wavelength policyconstraint that specifies an operator's policy information forwavelength assignment, and wherein the reply comprises an error messagethat indicates the PCE is not configured to calculate routing assignmentand wavelength assignment.
 6. A network component, comprising: a pathcomputation element (PCE) in communication with a path computationclient (PCC), wherein the PCE is configured to receive a request fromand send a reply to the PCC using PCE communication protocol (PCEP),wherein the request comprises: a lightpath constraint that indicateslimits on wavelength usage along a lightpath; and a wavelength policyconstraint that specifies an operator's policy information forwavelength assignment, and wherein the reply comprises an error messagethat indicates that the request is not compliant with administrativeprivileges.
 7. A network component, comprising: a path computationelement (PCE) in communication with a path computation client (PCC),wherein the PCE is configured to receive a request from and send a replyto the PCC using PCE communication protocol (PCEP), wherein the requestcomprises: a lightpath constraint that indicates limits on wavelengthusage along a lightpath; and a wavelength policy constraint thatspecifies an operator's policy information for wavelength assignment,and wherein the reply comprises an error message that indicates that aninternal policy of the PCE has been violated.
 8. A method implemented ina network component comprising a path computation element (PCE), themethod comprising: communicating with a path computation client (PCC);receiving a request from the PCC using PCE communication protocol(PCEP), wherein the request comprises a lightpath constraint thatindicates limits on wavelength usage along a lightpath and a wavelengthpolicy constraint that specifies an operator's policy information forwavelength assignment; and sending a reply to the PCC using PCEP,wherein the reply comprises a no path indicator that indicates that nolightpath was found.
 9. The method of claim 8, wherein the reply furthercomprises an error message that indicates the PCE is not configured tocalculate routing assignment and wavelength assignment.
 10. The methodof claim 8, wherein the reply further comprises an error message thatindicates that the request is not compliant with administrativeprivileges.
 11. The method of claim 8, wherein the reply furthercomprises an error message that indicates that an internal policy of thePCE has been violated.
 12. The method of claim 8, wherein the wavelengthpolicy constraint comprises a random assignment wavelength selectionpreference.
 13. The method of claim 8, wherein the wavelength policyconstraint comprises a most used wavelength selection preference. 14.The method of claim 8, wherein the wavelength policy constraintcomprises a least used wavelength selection preference.